Gavin Henson signed for Toulon today but he will not be eligible to play in their Heineken Cup quarter-final against Perpignan in April. The French club had hoped to register Henson as a "medical joker" in the Heineken Cup to replace the injured three-quarter Clément Marienval, who is unlikely to play again this season.

However, as Toulon were unveiling the 29-year old Henson at a media conference today, the organisers of the Heineken Cup, European Rugby Cup, were on the telephone to the club explaining that Henson was ineligible to play in European rugby's showpiece tournament for the rest of the season.

Henson is barred because he came on as a replacement for Saracens during their Heineken Cup defeat against Leinster in Dublin last month, his final appearance for the Watford-based club. He failed to finish the match after suffering a calf strain, an injury that is expected to clear up next week when he will start full training with Toulon.

"The rules are clear," said an ERC spokesman. "Once a player has been named in a match 23 for a Heineken Cup match, he may not play for another club in the tournament that season. He does not have to step on to the pitch. Gavin Henson is cup-tied and Toulon have been informed of that."

Henson should taste Top 14 action soon after he returns to fitness with the England fly-half Jonny Wilkinson away on Six Nations duty for the next seven weeks and the Argentina fly-half/centre Felipe Contepomi injured.

Yesterday Henson said the lure of playing alongside Wilkinson was just too great, while the Saracens chief executive Edward Griffiths defended his club over accusations that thje Welshman's signing was just a PR stunt in the first place. "It was just a massive opportunity for me. I couldn't really pass up on," Henson told BBC Wales. "Looking at a clause in my contract as well, and plus [director of rugby] Philippe [Saint-Andre] was really keen for me to play 12 at Toulon and starts straight away, so more or less start playing next week. And also cover 10 when Jonny's not there, and to obviously play alongside Jonny Wilkinson - 10-12 – that is going to be amazing.

"I couldn't really pass on this and obviously the weather is pretty good down here. I think it's going to be great for me and I can't wait to start on Monday with them."

On whether Henson fitted in at Saracens, Griffiths said: "That would be for him to say. From our point of view we're comfortable we worked as hard as possible to create the right environment for him.

"If Gavin feels his career lies somewhere else then under the terms of the arrangement we have with him he's perfectly entitled to do that. If he'd been signed in the wake of no injuries then you could have said it was a PR stunt but we're a rugby club, not a PR agency."